I'm writing a report with the sentence:

The vaccine has been shown to reduce diarrhea in an in vivo model.

Colleagues use a sentence starting with

The vaccine has shown to reduce...

In my opinion, the vaccine obviously didn't show anything itself, so it makes sense to use passive voice. What is your expert opinion?

  • 1
    Other parts of the phrase may change too. Compare "the vaccine has shown [it has] net positive outcomes" with "the vaccine has been shown to have net positive outcomes".
    – Henry
    Nov 17, 2023 at 10:42
  • 1
    You are right. Experiments or tests have shown what the vaccine does. Nov 17, 2023 at 11:00
  • I'm going with "The vaccine reduces diarrhea in an in vivo model." I know that painkillers reduce fever, maybe not with intent, but they do. Nov 17, 2023 at 14:28
  • This should never have been migrated. I spent several hours looking at it and still couldn't produce a definite answer. This has nothing to do with learning English, it is a difficult question about a domain-specific writing convention that has a long history.
    – Phil Sweet
    Nov 19, 2023 at 13:48

2 Answers 2


There are usages in the literature with and without (implied) volitional agents:

  1. Metformin has been shown to have encouraging effects on several metabolic aspects of polycystic ovarian syndrome ....

[implied volitional agent: 'researchers', say, in the by-phrase 'by researchers']

  1. Even a moderate amount of weight loss (5 - 10% body weight), before pregnancy, with or without metformin use has shown to be sufficient in improving metabolic markers.

  2. Use of metformin throughout pregnancy in women with polycystic ovary syndrome (PCOS) has shown to reduce the rates of early pregnancy loss, preterm labor, and prevention of fetal growth restriction.

[All from a single NIH_National Library of Medicine article] (examples re-ordered)

While passives, with or without specified agents (indicated in by-phrases), are unremarkable (sentence (1) above), the use of 'show to be' (example (2); compare 'prove to be') is less common, though quite acceptable. Other examples:

2a. The technique of selective photoaddition has shown to be very useful to obtain high single step enrichment factors.

[M Stuke; ScienceDirect; 1978 › article › pii › pdf]

2b. Despite vaccines, beating COVID-19 has shown to be tougher than expected.

[Mark Pattison; National Catholic Reporter; 2021]

2c. Mass spectrometry has shown to be an effective tool for the structural characterization of the synthesized compounds

[Chemistry Central Journal; Ludwig.guru]

The typical usage is of a technique proving to be effective/ineffective, but intransitive usages with human agents are found:

2d Throughout the years she has shown to be dedicated and proactive, whilst identifying gaps in processes and maintaining high standards.

[Bennett Business Partnerships]

These sound formal, which is probably why most examples are in say scientific writing.

When it comes to 'have shown to [verb]' with verbs other than 'be', though there is evidence of usage (eg examples (3, 3a, 3b))

3a Community monitoring, however, has shown to have little effect on teacher absenteeism.

[The New York Times]

3b Eigenfrequency with mode shapes has shown to have significant influence on transmitting-receiving characteristics of pMUT.

[Materials Science and Engineering: B],

“Programs that require human time and resources to implement them are difficult to scale, particularly in our current environment in the US where there is limited investment in prevention,” Fitzsimmons-Craft wrote, adding that the support of a human coach has shown to make prevention more effective. “Even though the chatbot was a robot, we thought she could provide some of that motivation, feedback and support ...."

[Lauren Aratani; The Guardian; May 2023]

the following Google 4-grams indicate that, while becoming more apparent after 2000, it is still comparatively rare:

enter image description here

Accordingly, I'd use the passive here, but it's over-prescriptive to object to the use of 'the vaccine has shown to reduce ...' in formal contexts. Language develops. And the argument vaccines can't show anything fails with 'the vaccine has proved to reduce ...', obviously acceptable even though vaccines neither appear at trials nor argue convincingly in debates.

  • 1
    If I were editing the examples without "been", I'd put it in., People (authors, who are poorly edited) repeat mistakes all the time.
    – Lambie
    Nov 17, 2023 at 14:19
  • 'Thou' was once the correct form. 'It is me' would have lost me a mark in an English essay when I was at school. Nov 17, 2023 at 15:33
  • Yes, you always manage to change topics. It is me or I was another question.
    – Lambie
    Nov 17, 2023 at 15:44
  • You changed the topic, from an actual case (shown to be in use, there being a credible number of well-written examples) to the general 'People (authors, who are poorly edited) repeat mistakes all the time' (implication, this is a mistake [because I say so]'. I've already said that I would personally use the passive here, but pointed out that 'correcting' the alternative would be over-prescriptive. Nov 17, 2023 at 19:45
  • Of course, I am saying there is a mistake because I say so. I don't believe correcting it is over prescriptive because without the passive it is funny (haha).
    – Lambie
    Nov 18, 2023 at 14:33

Using the passive voice is acceptable. However, many academic journals are starting to allow or encourage the active voice. It tends to be more direct and the sentences are shorter. Here's an example based on your sentence with the researcher's name made up:

Chen et al (2022) demonstrated that the vaccine reduced diarrhea in an in vivo model...

Multiple studies (Smith et al, 2022, Franks et al, 2021, Johnson et al, 2020 ...) showed that the vaccine reduced diarrhea in an in vivo model...

Yes, the vaccine didn't conduct the study or studies. However, someone did. The researchers can be considered the actors here.

  • But not all verbs can be used this way, which is the basis of the question. 'The vaccine was demonstrated to be very effective' but not 'The vaccine demonstrated to be very effective'. Nov 17, 2023 at 19:42
  • Sure, get rid of the passive if you can but don't write this: Despite vaccines, beating COVID-19 has shown to be tougher than expected. It makes little sense without a been.
    – Lambie
    Nov 18, 2023 at 16:49

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